So what caused the Sugar Land, Texas, garage fire this week that destroyed a Fisker Karma plug-in hybrid and two other cars?

The local fire inspector told Autoweek that the fire started in the Karma, but said he didn't know the exact cause. On Thursday, EV expert Jon Bereisa suggested to me that the Karma's cramped engine-bay packaging could have created conditions that led to the blaze.

Now Fisker Automotive has fired back, offering a rebuttal of Bereisa's speculation in a detailed statement to Automotive News.

As I noted in a Friday blog, Bereisa said the Karma's tight engine compartment packaging could result in a "thermal condition" and the car's possible inability to diffuse heat away from the engine bay and exhaust system.

Bereisa -- formerly chief engineer of the GM EV1 and systems architect of the Chevrolet Volt, and currently CEO of Auto Letrification LLC -- said: "That engine is shoehorned into that bay, because they had to use a larger engine, because it was too heavy a car. As a result, there's no room for exhaust routing and heat-shielding to route the heat away."

But Fisker says the thermal management of its Karma plug-in hybrid adequately diffuses heat in hot-weather and high-load conditions.

The company says the Karma passed safety certification following, "extreme testing of the vehicle, involving laboratory simulations of thermal incidents and on-the-road tests in extreme climate conditions… No incidents of any kind involving engine systems were found."

'Fully tested'

In the statement, Paul Boskovitch, Fisker director of powertrain, said: "Our technologies and engine design have been fully tested and certified at the highest level."

"It is irresponsible and ill-informed for technology pundits to suggest otherwise in order to secure media attention for unfounded claims," he said.

Bereisa said he doubted that the battery pack was to blame for the fire that burned the garage and house of Karma owner Jeremy Gutierrez.

But Fisker says: "Cooling algorithms have been developed to ensure that, at power off and under certain conditions, the vehicle cooling fan maintains circulation in the engine compartment in order to remove any excess heat.

"Packaging of the engine and surrounding components has been done within competitive benchmark standards and heat protection sleeves are placed on and around all hoses in or near high heat zones. All exhaust components have properly engineered heat shields and maintain the recommended separation distance between the shield, shielded components and affected components."

'Zero flammability'

Bereisa suggested that a fluid leak of gasoline, oil or coolant could have ignited under such hot operating conditions. But while many coolants contain glycol, a flammable compound, Fisker says it is "using DEX-COOL 50/50 coolant with a zero flammability rating, according to the Chevron Manufacturers Safety Data Sheet (MSDS) #10445."

As for the engine compartment layout, Fisker says: "The brake system booster which contains the brake system fluid is in a protected region behind the fender on the 'cold'side of the engine. The power steering pump and fluid are also located on the 'cold'side of the engine, near the front of the vehicle."

In addition, the cooling system of the Karma has been over-engineered to account for potential high-load situations, the company says.

"The engine power required at 125 mph (top speed) is less than 115 kw, well below the maximum capability of the engine for continuous operation. In addition the engine controls maintain a thermal watch of the engine and at a temperature of 117 [degrees Celcius] begins to limit power in order to maintain coolant temperature below this point. This is well below the engine manufacturer's recommended maximum temperature rating of 127 [degrees Celcius]."

The company also said that the engine was designed "using the latest Computational Fluid Dynamic (CFD) software packages."

"Evaluations of the results were performed both by the Fisker Thermal team and external consultants. Testing involved thorough road and lab exercises, including multiple hot weather trips over thousands of miles of incident-free operation in Death Valley and Palm Springs, Calif. Additional testing was also performed successfully at maximum and sustained speeds [125mph] on the Autobahn in Germany."

Wind-tunnel testing also mimicked conditions in the Middle East and Africa, according to Fisker.